In the tutorial from openstack.org says keystone endpoints should be set to something like http://HOST_IP:8774/v2/%(tenant_id)s what does '%(tenant_id)s' here mean? Because in a lot of forums, I saw the endpoints are something like http://HOST_IP:8774/v2/$(tenant_id)s What does this '%' and '$' mean here; even, someone suggests to set endpoints exactly as http://HOST_IP:8774/v2.0.